Sprocket wheel



May 22, 192s.

E. L.l F lRTH SPROCKET WHEEL Filed Aug. l, 1927 3 Sheets-Sheet 1 May 22, 1928. 1,670,718

E. L. FIRTH sPRoCKET WHEEL Filed Aug. l, 1927 2'; Sheets-$11991.. V 2

May 22, 1928. 1,670,718 v E. l.. FIRTH SPROCKET WHEEL Filed Aug. l, 192'? 3 Sheets-Sheet 5 Patented May 22, 1928. l

,UNITED STATES LIMITED, or Hounslow, ENGLAND.'

Application filed-'August 1, 1927,"S.eria11\To.

This invention relates to sprocket wheels and more particularlytof'the'- type in which the teeth proper are :formed` on .theendless link or other-meinberfzandengage ,grooves or'elements on thesprocket constituting the teeth or drivingy surfaces. y

Insuch: sprocket wheels it :has been? found, f and especially in the case of endless trackv vehicles to which'type of sprocket wheel this.

invention more particularly. frelates, v that aftera certain amount ofusejtl-iegrooves v Y lthe teeth `are constructed of a'number-of-eeleor yelements constituting the teeth or drivingl surfacesv become worn, asfalso doesl that -part'or parts ofthe sprocketupon which theI chain or other endless linkf members.` rest.

In this. connection'it should beffnoted'that in conventionaly chainrdrives,fth`e usual practice is that those'zelements of thesprockety which drive the vcha'innand -that part or parts of the vsprocket upon Vwhich the chain rests, or upon whichthe articulated plates attached to therchain rest, `(as fin the c'ase lof endless track vehicles) arefone and-the same. v

`IVe have-found, however, and especially in the inserted toothtype of-spro'cket,nthat these two Aelements are functionally sepa-k rated, that is,`tlie teethgdrive zand driveonly, while a separate diameter. is-provided on the sprocket for Vthe fsupportof the chain or articulated plates forming theitrackshoes. f It is therefore, I necessary i inl order f to obtain accuracy of drive? to `co-ordinate these .two 4functionally i separated 'elements 'by making .a relative i adjustment .between the` sprocketl teeth and that'part orpartsrofthesprocket,'

lhereinafterreferred tov as'the sprocket diameter, supportingthe track'plates which :form the shoes, notmattervf'how carefullyfthis relationship may be 'calculated beforehand, lit is impossible to "arriveat theexact di-l mension Yof lthe 'sprocket diameter on which the 'track plates are supported, and-unless correctness in pitchbetweenthe cha-in and the sprocket' is obtained, theidrive isineftlcient. 4taking down of the fsprocketfandr theladju'st-y v mentfof the diameter. Theamount@of'adj ustment required being sometimes.y as .small as l'3/1O0ths of an inch, which, 'Jhowever, makes all lthe dierence `:in thef correct 'meslv ing of theV teeth. y Further, after thetvehicle v.has been run `for some ftiinewand tbe-link# In practice, this lnecessitates the y ameter and :adapted .to y engage and support 209,961, ana'inereat Britain May.3,i92e.-

joints have. worn, therebyr increasing theL `pitch of the chain, :similar trouble .occurs andit is-necessaryagain toadjust the drive.'

One of the objects of the invention -isthe construction of .a sprocket wheel ;inwhich .theteeth may easily be renewedanda Ifurther object Vconsists in' the provision oft-a .sprocket where adjustahilityof the pitch vof the lteeth Aand sprocket diameter `may be obtained. f

According 'toone ,feature of` this .invention l ments having similar surfaces kadapted to be fixed 1n succession` in' the i operative position,V

a fresh surface being'ymoved into-the .opera-7 tive position when the othersurface ips-.worn

5 #In one embodiment 4of .theinvention the sprocket wheel comprises itwo plates `ing-each of which are' formed a plurality of pairs VVVof .holes forming bearingso'ckets in which are mountedl the 4elements constitutingthe teeth or driving surfaces; the metalfb'etween `the 'holes being cut away .in order .to allow of the insertion of teethl which; may `consist of. bars of `square section h-a.ving.;grooves j whose bases engage .withthe holes formed-in the sprocket plates. Preferab'lythe holes inthe plates aresemi-circu'lar whenthe bases vofthe grooves are circular, to facilitatezm-anf ufacture..l

Theteeth are held in positionfjby'bolts,

.each bolt. .having .two surfaces `which engage aA surfaceon eachvtoothfthe bolt being securedbv a `screw nut, between v.which land the teeth. 1

AThe operative .surfacefof the teethinay. be other than planesince the` surfacesmay LAccording :to another feature .of theta inthey track yor l. otherI` endless link Jmember, and means. for .iefecting .the .adjustment ofl ;said members;l

' .In onefconfstructionfa numbrxofggboltsgiay :be provided mounted .on the `periphery .of

the :sprocket and `located .interina ate,v Athe .theteeth is aplate havingfedgeslsobevelled asto make good contactv with the; surfaces-.of

be cycloidal, and the cross, section: of .theqb'ar i may be triangular v or polygonal.

' may be located so as each to engage the ly effected. v

ends of adjacent links, and for this purpose may be Y-shaped, the arms of the Ys engagingV the two'ends of yan adjacent pair'of links.

According to a further feature ofthe in vention thefsprocket teeth alone orfin con rjunction withfthe sprocket diameter is or are adjustable as to pitch.

They sprocket" teeth maybe adjustably mounted in radial slots formed in'the -periphery ofthe sprocket wheel, and in one construction pairs of adjacent teeth may be Amounted in a series of plates adjustably carried by the sprocket wheel. The plates may beset according to the pitch required by 'means of cam surfaces formed on pins, car

ried by 'the sprocket and the transverse --i'novement of. which in onev direction,'cause the plates to move outwardly.

The plates mayl be provided with track f plate `or other endless link member engaging surfaces which formv the"diameter of 'the sprocket yso that on the adjustment -of the fplates,adjustment ofl pitch'of the sprocket lteeth and sprocket diameter is simultaneous- It should be understood'that the variation of the diameter of that part ofthe sprocket upon which the articulated plates bear does not and cannot invefect alter the pitch of rthe chain, i. e.,fthe pins and yetby altering this Adimension the pitch of the chain can be brought'into harmony with the pitch of the sprocket Whether this adjustment'is calledy 1 for by initial inaccuracies in manufacture or byan increase of the pitch of the chain due to wear. The reason for this seeming anoin- 4 `aly is that the teeth on the sprocket owing to their form have a variable pitch circle 'which is decided by the diameter of that part of the sprocket upon which the plates attached to the chain bear.y The form of sprocket teeth employed in these cases is similar to that used in .silent-l chain practice where the relationship between the Vpitch of the chainand the sprocket is harmonized owing to the fact that the chain automatical ly ride-s out on the pitch diameter of the sprocket. .It will be seen, therefore, that sprocket diameter which supports the chain and it'is therefore, not essential alsoto provide for the radial adjustability of the sprocket teeth, although this may, if desired,`

be done.

The invention is illustrated in the accompanying drawings as applied-to ka sprocket wheel particularly adapted for driving the tracks of endless track vehicles, in which Figure 1 is an elevation of a part of a sprocketwhe'el, Figure 2 a vertical section on the line 2 2 of Figure 1, and Figure 3 a. sectional view on the line 3 3.

Figure 4 is an elevation partly in section `showing one method` ofA adjusting the sprocket diameter, Figure 5 being a sectional view thereof, on the line 5 5, Figure 4. Figure 6 is an elevation of an alternative method of adjustment. j Figures 7 and 8 are respectively an elevation and section showing amethod of adjust ing both the sprocketJ teeth and sprocket diameter simultaneously. Figure 9 is a detail view. f

Referring to the drawings, the sprocket wheel is formed from two plates a, having semi-circular holes b cut in4 pairs around their periphery, the metal between the holes being cut away as at c to allow for the insertion of bar element-s d forming the teeth or driving surfaces.

The elements d are shown asv'being of .square section, but maybe of any polygonal section, or the driving faces instead of being plane may be cycloidaly or of any other suitable curved surface. They are formed with grooves e with circular bases to conform to the circular holes b, with-which they engage, being held in position by bolts f. The heads of the bolts f are provided with surfaces g adapted tolie against the faces of the elelments` d, which are secured between the sur faces g and similarly bevelled surfaces 'z' on plates L, by means of nuts i Rubber or other `resilient blocks [Z are placed in sockets m in the heads of the `bolts f and serveto lsilence the track. i

` When one driving surface has become worn, a fresh one may be brought into play by merely slackening off the nuts la' until the kelements on bar-s' @Ld arel freelyk rotatable.

Referring now to Figures 4 and 5, the sprocket wheel is indicated at 1, and 4 are the renewable driving teeth. Mounted in bosses 14 formed'V on the sprocket 15 are plates for setting the teeth.

The links of the track are shown at 16 and the plates forming the track shoes at `17, provided with flats 18 at each side thereof for engaging the diameter of the sprocket which in Figures 1 and 2 is .shown .at 19.

In Figures 4 and 5, the sprocket is provided with a plurality l of boltv members around its two peripheries,vone pairof which is shown at 20, and `which are adjustably held in screwed sockets 21, 22 being nut members by means of which they are se- The heads 23 of the bolts constit-ute the parts of the sprocket, referred to as the diameter, supporting the track shoes by engagement with the flats 18, and which diameter is, therefore, adjustable. 2i are projections on the sprocket adapted to engage the track shoes and limit their movement.

Referring to Figure 6, a similar construction is shown, except that instead of the l bolts 2O being located on the sprockets so as to engage the centres of the track shoes, they engage the ends thereof. For this purpose,

the heads 23 of the bolts are Y-shaped and.

sprocket diameter by screwing or unscrew-v ing a nut on the screwed end of the head 31 of the pin 28, engaging a'bracket 32 carried by the sprocket, and through a hole iny which the head 31 is passed. The plates 26l are slotted at 33 to embrace the pin 28, the

ends of the slots 33 engaging the cam surfaces 27.

The ends of the driving elements Il are 1mounted in holes in the plates 26 as indicated at 34, and are formed with squared portions 35 which engage slots 36 in the peripheries of the sprockets and by means of which the position of the elements may be set. l

It will be seen, therefore, that by screwing or unscrewing the nut 30, the pin 28 may be moved transversely, the plates 26 being caused. to move outwardly or inwardly, whereby the sprocket teeth and sprocket diameter may be simultaneously adjusted.

y What I claim is L- 1. In a sprocket wheel comprising two hub plates having corresponding series of holes formed around their peripheries the combination with a plurality of polygonal bar elements forming the sprocket teeth, of means for mounting said elements in pairs in 'said holes andl for setting them with their surfaces in correct driving position.

, 2. In al sprocket wheel comprising two hub plates .having corresponding series of holes formed in pairs around their peripheries, the combination with a plurality of polygonal bar elements forming the sprocket teeth and having grooves with circular bases, of means j for mounting pairs of said elements in their respective holes and means engaging one of the free surfaces of a pair of elements for setting them in correct driving position.

3.v In a sprocket wheel comprising two hub plates having corresponding series of holes formed around their peripheries, the combi'- 1 nation with a plurality of polygonal bar elements forming the sprocket teeth and having grooves with circular bases, of pairs of semi.- circular recesses in the sides ofsaid holes for receiving the grooved portions of said elements, and bolts whose heads are provided with bevelled surfaces adapted to engage a free surface of each of said elements `for holding them in correctfdrving position.

4:. In a sprocketwheel comprising two hub plates having corresponding series of holes formed aroundtheir peripheries lthe combination with a plurality of polygonal bar ele-V ments forming the sprocket teeth, of means `for mounting said elements in pairs in said holes and for setting them` with their sur-` faces in correct driving positionand adjustable means mounted adjacent the peripheries of the hub platesv for correcting the sprocket diameter. y

In testimony that 1 claim the foregoing as my'invention I have signed my name this' 21st day of July 1927. v j

EDWARD LioNEL' riirrii. 

